There are many, many different forms and shapes of window frame members generally made by extrusion aluminum or polyvinylchloride (PVC) that are connected together to form the window frame for mounting windows in position in the window opening.
U.S. Pat. No. 5,666,773 issued Sep. 3, 1997 to Librande et al. shows a number of different arrangements of extruded materials and their fabrication to form window frames. This patent discloses a tapered spacer element to mount a frame element on a sloping sill and uses extruded trim members to connect to the frame to trim the window frame to the surrounding wall structure.